The Big Four is a work of espionage-detective fiction by British writer Agatha Christie, first published in the UK by William Collins & Sons on 27 January 1927, and in the US by Dodd, Mead and Company later that same year. The book is the fourth of thirty-three full-length novels featuring her detective Hercule Poirot. It also features Poirot's colleague, Arthur Hastings, and Inspector (later, Chief Inspector) Japp.